Just forget the solution presented. Its pretty straight forward and we don't need iptables or ettercap.

Just activate ip forwarding in debian and start sslstrip. All we have to do is use proxy settings in OWB.The benefit of this way is that we can configure specific URL settings in OWB and use the HTTPS downgrader on demand. So we can f.e. configure it in a way that only Youbtube will make use of it.

1. enable IP forwarding Code:

echo "1" > /proc/sys/net/ipv4/ip_forward

2. Start sslstrip Code:

sslstrip

3. change proxy settings in OWB. Just enter the IP of our debian machine and use port 10000